Well, bathroom sink was running slow. Did the plunger, hot water,
baking soda/vinegar, Liquid plumbr. It was running slightly better,
but still slow. Keep running hot water down over a two-week period, no
better.

So, plunged the heck out of it today. Now it is really clogged....

Took off the trap, which was clean. Took off the tailpipe, which
connects to a 1"1/2 CPVC (or whatever that black plastic stuff is)
inside the wall.

Just inside the wall the plastic pipe makes a sharp "L" to the right.
I tried my 3/8" snake and then tried my smaller "plumber's tape."
Cannot get past the L just inside the wall.

I can feel a great amount of cold air coming in from the open drain
pipe, which I assume is coming in from the vent? I was thinking of
going on the roof and trying to snake the vent....All I have is a
manual 25' snake, and it is a two story house and the clogged drain is
on the first floor, although I guess I can rent a longer snake.....Is
it worth it?

Should I throw in the towel (so to speak LOL)....and call a pro....